Digital communication systems are known which utilize orthogonal frequency division multiplexing (OFDM) modulators/demodulators to modulate and demodulate quadrature amplitude modulation (QAM) coded signals. In OFDM, data is transmitted in parallel using orthogonal sub-carriers, and an equalizer functions to compensate for channel distortion in each sub-channel.
OFDM has been increasingly adopted in high-speed multimedia data transmission systems (e.g., digital broadcasting). Exemplary systems include x digital subscriber line (xDSL), Wifi, Wimax, digital multimedia broadcasting (DMB), digital video broadcasting terrestrial-handheld (DVB-T/H), and integrated services digital broadcasting-terrestrial (ISDB-T).
OFDM communication systems exhibit reduced communication errors and relatively high communication quality by executing synchronization between a transmitting signal and a receiving signal before data transmission/reception between a transmitter and a receiver. Usually, synchronization functionality in OFDM communication systems is separated into frequency synchronization for equalizing the carrier frequency of a transmitter with that of a receiver, and time synchronization for determining a start point of an OFDM symbol.
However, even when exact synchronization is accomplished at the beginning of transmission/reception, the start point of a symbol drifts with the lapse of time. This is because a sampling clock of a transmitter is not (and cannot) be the same as that of a receiver. The result is a sampling offset which must be periodically compensated for in the synchronization scheme. This is done by periodically sending a recognizable symbol to the receiver, or by sending a pilot signal to the receiver whose position is recognized by the receiver. The receiver utilizes the symbol or pilot signal to estimate a sampling offset. However, this approach suffers a drawback since external signal interference (e.g., analog broadcasting signals) can introduce errors in the symbol or signal received by the receiver.